In the past, colored lamps have been made by placing a colored filter in front of a continuous spectrum tungsten filament lamp. The vast number of available filters makes almost any color possible. Unfortunately, tungsten filament lamps are not efficient, particularly when filtered; nor are they durable in comparison to discharge lamps. Discharge lamps can be much more efficient, and have a much longer life than a tungsten filament lamp. For example, a neon discharge lamp is presently being used on the Ford Explorer as a central high mounted stop lamp (CHMSL). The lamp has a 3.0 millimeter inner diameter, a 5.0 millimeter outer diameter, a low pressure neon fill, and a 47.10 centimeter arc gap. The lamp is driven by a 60 kHz sine wave and generates 220 lumens with an efficacy of 8 lumens per watt. It is expected to last for two thousand hours of operation, and eight hundred thousand starts. A typical neon emission spectrum is shown in FIG. 2.
Discharge lamp colors are the result of particular atomic emissions and are adjustable only by selecting different chemical compositions. Possible lamp colors are then determined by the limited number of useful gases, and phosphors, where a phosphor is used. Not all colors are available, nor are all colors efficiently produced. There is then a need for a method of operating discharge lamps that enables color tuning, while still operating efficiently.